Medical gases

Understanding the complex process of production, storage and delivery of medical gases is vitally important to ensure safe and efficient practice by anaesthetists. This article discusses the medical gases commonly used in anaesthesia and intensive care, and details the journey of the commonly used medical gases from production to patient delivery. It includes core knowledge for the FRCA.     

Medical gases,their storage and delivery

Medical gas production, storage and delivery is a complex process. Design of such a system must ensure that gas delivery is safe, convenient and cost-effective. This article reviews the production, storage and delivery of commonly used anaesthetic gases, following the gases from production to delivery.     

European normative recommendations for medical gas pipeline systems

Several recent decisions have been made in order to increase the security of medical gases delivery in French hospitals. These different changes affect: 1) the hospital itself with the creation of working groups in charge of both monitoring and maintenance of gases networks; 2) the pharmaceutical regulation with promotion of several gases to the status of drugs or need of CE marking for the whole gas network. European rules onset required to give up French former norms (NF) to the profit of "NF EN" rules. Nevertheless, the new norm NF EN 737-3 which concerns medical gases distribution systems does not affect principal clauses of the previous NF S 90-155. It introduces new elements allowing to deploy two types of medical gases networks: the double pressure level used in France and the single pressure level used in the rest of Europe. This new norm, which attempts to harmonize alarm control systems in both types of networks, suffers from important limitations describing the double pressure level systems. Lastly, the final checking proposed by this new norm is very different from the previous one, and is likely to be problematic for the final users within the hospital.     

Electrosurgery

Electrosurgery is used clinically for coagulation, cutting, desiccation and fulguration of tissue. The principle of heat production by passing electrical current through tissue is modified to produce these effects. Monopolar and bipolar electrosurgical circuits are most commonly used. The monopolar circuit requires electrical current to flow through the human body, whilst in the bipolar system the current flows from one tine to the other through the tissue held by the forceps. Complications of electrosurgery include burns, risk of explosion if combustible gases are used, interference with pacemakers and production of surgical smoke.     

Nitric oxide: description of a pipeline delivery system

We describe a pipeline system suitable for the delivery of nitric oxide gas to an 18-bed intensive care unit. The pipeline was developed and installed according to the current UK regulations HTM 2022, which relates to the supply of piped medical gases. Where HTM 2022 did not specify the appropriate standard, we consulted widely to achieve a safe solution. We continue to monitor all aspects of the performance of the pipeline to ensure safe operating practices and recommend changes to the standards.     

Medical gases,their storage and delivery

Medical gases used in anaesthesia and intensive care include oxygen, nitrous oxide, medical air, entonox, carbon dioxide, heliox and nitric oxide. Breathable gases administered to patients are stored either in bulk outside the hospital or in cylinders within the hospital. Medical gases are then distributed throughout the hospital via a pipeline network.     

Social problems in pregnancy

Socioeconomic deprivation adversely affects health and access to healthcare. It is closely associated with problem drug use, which exacerbates the medical and social effects of poverty, and is associated with several medical problems including dental caries, vascular damage, thromboembolic disease and blood-borne virus infection. Problem drug use has increased markedly during the past 20 years, especially among women of childbearing age. In addition to the widespread use of cannabis, the drugs most commonly used in the UK are methadone and heroin, amphetamines and benzodiazepines, while use of cocaine and crack cocaine is increasing. While heroin can cause preterm delivery and some drugs (opioids and benzodiazepines) can cause withdrawal symptoms in the baby, most of the medical effects of drug use on pregnancy are indirect. Blood-borne virus infections, including HBV, HCV and HIV can be transmitted by sharing injecting equipment and can be passed vertically from mother to baby. Women from socially disadvantaged backgrounds have potentially high-risk pregnancies in medical and social terms, but can have difficulties accessing appropriate care. In view of their many problems, they need multidisciplinary care that addresses all their medical and social problems and is appropriate in content, design and delivery.     

A new humidifier.

A new heated water-bath humidifier operates on a new basic principle which overcomes the practical disadvantages of existing systems. A heated hose is used to control a temperature drop along the whole length of the delivery line instead of raising the temperature of the gases in the delivery line as in previous systems. Therefore the tank does not have to fully saturate the gases and a simple, totally cleanable design is possible. A temperature sensor at the delivery point controls the hose heater, constituting a rapid response, low thermal inertia system and delivery temperature is displayed on the unit. Compensation for varying gas flows and ambient temperature changes is inherent and the unit is suitable for neonatal/paediatric and adult use without special adjustment. The tank has a separate reservoir chamber which feeds an evaporation chamber via a cleanable float valve, conferring many advantages including clearly visible water levels, easy filling without breaking the circuit and constant compression volume. Full fail-safe alarm systems are incorporated.     

Fluorocarbons

This article presents information on medical applications of fluorocarbons. These inert chemicals have a high solubility for the respiratory gases and, in emulsified form, are present in the oxygen-transporting plasma substitutes now undergoing clinical trials. Oxygen content is directly related to arterial partial pressure of oxygen (PaO2). Thus, although oxygen transport of Fluosol-DA 20% (FDA) is only 0.75 ml per 100 ml per 10 kPa, oxygen delivery at the tissues will be adequate in the presence of a high PaO2. FDA has a low viscosity at low shear rates and this, together with a very small emulsion particle size of 0.1 micron, helps provide improved tissue oxygenation in conditions of ischaemic hypoxia. Fluorocarbon plasma substitutes may be employed as 'blood', but may also be used for a wide range of purposes in clinical practice. This review describes some current and potential future applications.     

Patients understanding of terminology commonly used during combined orthodontic-orthognathic treatment

BackgroundCommunication between patients and clinicians plays an important role in improving quality of healthcare and clinical outcomes and ensuring that patients understand medical terminology used by their physicians is a core aspect of this. The aim of this study is to evaluate the degree of patient understanding with respect to commonly used terms in a joint orthodontic-maxillofacial clinic in the context of preparing for combined orthodontic/orthognathic treatment.MethodsPatients were recruited to partake in a short two-part questionnaire. Demographic data collected included participants’ age, sex, level of education, fluency of English and whether English was their first language. In the second part of the questionnaire, participants were asked to identify the correct definition of 11 commonly used terms from a series of multiple-choice answers.Results51 patients participated in this study ranging between ages 15 to 52. 86% of patients selected English as their first language and 37% reported having a university education. The overall mean score for the questionnaire was 44%, with the best understood term being ‘retainers’ at 80% correct and ‘decalcification’ the worst understood at 14% correct. An association between level of education and understanding of specific terms was detected.ConclusionThis study highlights the overall sub-optimal patient understanding of medical terminology used by clinicians on a joint orthodontic-maxillofacial orthognathic clinic. The authors of this study recommend further consideration to the terminology currently used as well as adapting the mode and frequency of information delivery, serving to improve patients’ understanding and retention of medical conversations.     

Melted delivery hose — a complication of a heated humidifier

The polyvinylchloride delivery hose of a Fisher & Paykel dual servo heated anaesthetic humidifier was melted by the intraluminal hose heater, causing a major leakage of anaesthetic gases during a surgical procedure. Under experimental conditions, melting could be reproduced using polyvinylchloride but not polyester elastomer tubings. Only tubings made of materials with high melting point should be used as delivery hose in heated humidifiers with hose heaters.     

Facial edema and pruritus after intravenous injection of midazolam

Midazolam is a short-acting benzodiazepine commonly used for conscious sedation for a variety of procedures. Severe adverse reactions, including respiratory depression, respiratory arrest, and anaphylactoid reaction, have been described by manufacturers. We report a patient who developed facial edema after iv injection of midazolam during caesarian section. A 26-year-old woman with a history of atopy and pollen allergy was scheduled for caesarian section. Spinal anesthesia was induced with bupivacaine without significant medical problems. Shortly after receiving 2 mg of iv midazolam 15 minutes after delivery for conscious sedation, she developed pruritus and severe facial edema. Airway obstruction did not occur and no specific medical treatment was necessary. However she was not able to open her eyes for 8 hours because of severe eyelid swelling. We should be more careful in administering midazolam which is generally regarded as safe and well tolerated.     

A MICROPROCESSOR-CONTROLLED GAS MIXING DEVICE

This paper describes the use of solenoid valves for the productionof binary gas mixtures. The system is controlled by a microprocessorand is capable of delivering accurate flows and concen-trationsof gases over the ranges commonly used in anaesthesia. Sincethe flow produced by the valves is pulsatile, a system for mixingthe gases and smoothing the pulses is described. A back pressureregulator is fitted downstream of each of two mixing/dampingchambers and a method of using this as a flow transducer isdescribed. The advantages of this system over conventional rotametersare discussed.     

Neonatal welfare and placental transfer of fentanyl and bupivacaine during ambulatory combined spinal epidural analgesia for labour

To investigate current concerns that potent opioid drugs, such as fentanyl, used for labour regional analgesia may affect neonatal status, maternal and umbilical plasma concentrations of fentanyl and bupivacaine at delivery were measured in 40 nulliparous patients receiving low-dose combined spinal epidural analgesia. Neonatal assessments included Apgar scores, umbilical blood gases and neurobehavioural tests. All maternal and umbilical venous plasma concentrations were low. Maternal and umbilical vein total fentanyl concentrations increased with increasing doses of epidural fentanyl ( r  = 0.46 and 0.30, respectively, p < 0.01). There were no significant differences between maternal and umbilical venous plasma total or free concentrations of fentanyl. Mean umbilical vein/maternal fentanyl ratios were 1.12 for total drug and 1.20 for free drug and values were unrelated to the last epidural bolus to delivery interval ( r  = 0.12, p = 0.49). There were no correlations between Apgar scores, umbilical blood gases or neurobehavioural scores and umbilical venous concentrations of either fentanyl or bupivacaine. The dose of fentanyl used for ambulatory combined spinal epidural analgesia would appear to have a negligible effect on neonatal condition.     

The SiBI connector: a new medical device to facilitate preoxygenation and reduce waste anesthetic gases during inhaled induction with sevoflurane

IMPLICATIONS: The SiBI connector is a new medical device used for vital capacity inhaled induction with sevoflurane. It allows efficient preoxygenation of patients and reduces waste anesthetic gases in the operation room during induction.     

Newer techniques of labor analgesia

In maternity units in which central neuraxial techniques are frequently used, newer methods of epidural drug delivery (continuous infusion, patient-controlled) are well established and combined spinal-epidural analgesia is commonly used. Continuous spinal analgesia has reemerged as a useful approach after accidental dural puncture. Lumbar sympathetic block has been revisited and the safety of paracervical nerve block improved. The analgesic properties of systemic opioid in labor are poor, but PCIA at least has psychological benefits and allows rapid drug titration. PCIA is again under investigation because of the potent antinociceptive effects of the short-acting mu-opioid agonist, remifentanil. The premixing of nitrous oxide and a subanesthetic concentration of volatile anesthetic for patient-controlled administration has been tested under control of midwifery staff and without direct medical supervision.     

Role of the surgeon in quality and safety in the operating room environment

Medical errors in the OR can result in substantial morbidity, poor functional outcomes and mortality. They are associated with significant increases in direct and indirect healthcare costs. In addition, errors in the OR associated with harm often have a profound negative impact on the patient, their family, and the medical providers’ psychological and social well being. The majority of medical errors are believed to be preventable. Rarely, an error is the result of an isolated single failure in the delivery of care. More commonly, multiple linked processes contribute to the error. Poorly designed systems of care delivery, poor information and knowledge transfer, ambiguous communication between providers and poor coordination of care are frequently identified as the underlying drivers of errors. Solving the problem is as complex as the causes. Raising awareness that an error is more than an individual’s problem or behavior is the first step toward a solution. Thoughtful planning in developing systems of care delivery through optimizing and leveraging the knowledge of the team members that provide care is the single most important defense against medical errors. Surgeons play an important role in facilitating the development of and empowering the teams they work through their active participation and effective leadership within the operating room team.     

Neonatal acid-base status following general anesthesia for emergency abdominal delivery with halothane or isoflurane.

STUDY OBJECTIVE: To determine whether halothane or isoflurane as anesthesia for emergency abdominal delivery is associated with better fetal acid-base parameters. DESIGN: Randomized study. SETTING: Inpatient Level III perinatal referral center in a university hospital. PATIENTS: Sixty-six gravidas undergoing emergency abdominal delivery under general anesthesia for fetal distress. INTERVENTIONS: Randomization to receive halothane or isoflurane at 0.7 minimum alveolar concentration as part of a standard anesthetic technique. MEASUREMENTS AND MAIN RESULTS: Umbilical artery and vein blood gases were obtained and compared for hydrogen ion concentration, partial pressure of carbon dioxide, partial pressure of oxygen, and base deficit. There were no significant differences between the isoflurane and halothane groups. CONCLUSIONS: There is no difference in the frequency or severity of acidosis associated with isoflurane or halothane when used for general anesthesia for emergency abdominal delivery of a distressed fetus.     

What is optimal flow and how to validate this

Since the introduction of cardiopulmonary bypass, clinicians have tried to define the optimal blood flow for a given patient. The difficulty in determining a correct blood flow lies in the fact that cardiac surgery is done in a very inhomogeneous population, from neonates to the octogenarian, and often under non-physiologic conditions (hypothermia, hemodilution, low flow, etc.). Although clinicians acknowledge that maintaining a minimum oxygen delivery is more meaningful than using a fixed flow rate based on the metabolic needs of awake resting volunteers, the latter is most used in clinical practice. This is explained by the fact that no values are available on critical oxygen delivery for adequate tissue oxygenation under a given clinical condition. This was an overview of the relevant literature. In most centers, perfusionists use in-line monitoring, such as venous saturation or venous blood gases, for estimation of adequacy of tissue perfusion. Unfortunately, these oxygen-derived parameters have a poor correlation with anaerobic energy supply. Measurement of intermittent whole blood lactate concentration is used to compensate for this poor relationship, but as it monitors the concentration at given time points, it precludes optimally timely intervention by the perfusionist. The physiologic buffering by bicarbonate of the acid generated by converting pyruvate into lactate will produce carbon dioxide. As a consequence, carbon dioxide-derived parameters do have a good correlation with inadequate tissue perfusion. In-line monitoring of carbon dioxide production gives real-time information on tissue perfusion. Use of a standard reference flow for each patient is a poor option, because it does not reflect the metabolic need of the patient. Oxygen-derived parameters, such as venous saturation or partial venous oxygen tension, are poor predictors of anaerobic metabolism. A combination of intermittent whole blood lactate measurement with carbon dioxide-derived parameters predicts anaerobic energy production and allows proactive intervention by the perfusionist.     

Anaesthetic breathing systems

A breathing system is a series of components that allows the delivery of oxygen and other anaesthetic gases to the patient as well as aiding in the removal of carbon dioxide. There are key elements that feature in all anaesthetic breathing systems with numerous classification systems used. The layout of individual breathing systems determines their clinical application and use. All of the above will be discussed further in this article as well as a brief summary of the use of carbon dioxide absorbers and their function.